Process for producing bulky paper

ABSTRACT

A process for producing bulky paper comprising the steps of transferring a fiber web ( 2 ) having a water content of 50 to 85% by weight to a patterning zone having a perforated patterning net ( 31 ) revolving along a suction unit; patterning the fiber web ( 2 ) in conformity to the perforated patterning net ( 31 ) by sucking the fiber web ( 2 ) which is held on the perforated patterning net ( 31 ) while applying 5 kcal/kg or more of heat to the fiber web ( 2 ) in a heat application zone simultaneously with or before or after the sucking of the fiber web ( 2 ); and then drying the fiber web ( 2 ) in a drying zone to obtain patterned bulky paper ( 3 ).

This application is the national phase under 35 U.S.C. §371 of PCTInternational Application No. PCT/JP99/04188 which has an Internationalfiling date of Aug. 3, 1999, which designated the United States ofAmerica.

TECHNICAL FIELD

The present invention relates to a process for producing bulky paperwhich is preferably used as an absorbent base, etc. of cooking paper,paper towels, tissues, paper products for cleaning, sanitary materials,and the like.

BACKGROUND ART

Conventional papermaking techniques include a process comprising forminga fiber web by use of a smooth paper layer-forming belt or carrier belthaving fine openings and uniformly pressing the fiber web for dewateringand a process comprising drying the fiber web by passing in hot air of athrough air drier without pressing for dewatering. However, theseprocesses have not achieved appreciable increases in paper thickness,water absorption capacity, and the like.

Known processes of producing bulky paper comprising imparting a patternby suction to a wet fiber web before being dried, passing the fiber web(not compressed) in hot air to half dry, and finally drying in a Yankeedrier include a process using a perforated patterning carrier belthaving 100 to 3600 openings each having an open area of 0.0072 mm² to2.1 mm² per 6.45 cm² (see Japanese Patent Application Laid-Open No.21405/77) and a process using a composite perforated patterning carrierbelt composed of a perforated patterning resin with prescribed openingswhich is prepared by using a photosensitive resin and a conventionalpapermnaking carrier belt which reinforces the resin (see JapaneseLaid-Open No. 5-506277 and Japanese Laid-Open No. 5-506893).

The process disclosed in Japanese Patent Application Laid-Open No.21405/77 is incapable of directing softwood pulp having a relativelylong fiber length toward the openings to form low-density projections.

According to the processes disclosed in WO 93/506277 and WO 93/506893,if the open area of the perforations is less than 3 mm², the low-densityprojections formed by suction have an insufficient volume for obtainingsufficient thickness, water absorption capacity, and softness. Further,because the resin part of the perforated patterning carrier belt isrubbed with many reverse rolls and the surface of a Yankee drier under astrong pressure, the processes are disadvantageous from the standpointof belt life. Furthermore, much time is required to remove or change thebelt, and it is infeasible to alternate the manufacture of plain paperand bulky paper or to easily alter the pattern of bulky paper.

DISCLOSURE OF THE INVENTION

Accordingly, an object of the present invention is to provide a processfor producing bulky paper having a large thickness, good absorption,excellent softness, and moderate strength.

Another object of the present invention is to provide a highlyproductive process for producing bulky paper.

Still another object of the present invention is to provide a processfor producing bulky paper which copes with long-term continuousoperation and allows the system to be switched to general papermaking orallows the pattern to be altered easily.

The present inventors have found that the above objects are accomplishedby carrying out patterning in a patterning zone having a perforatedpatterning net in a specific stage of the bulky paper production processwhile applying a specific quantity of heat.

The present inventors have also found that the above objects areaccomplished by carrying out patterning in a patterning zone having aspecific perforated patterning net in a specific stage of the bulkypaper production process.

The above objects are accomplished by providing a process for producingbulky paper comprising the steps of transferring a fiber web having awater content of 50 to 85% by weight to a patterning zone having aperforated patterning net revolving along a suction unit; patterning thefiber web in conformity to the perforated patterning net by sucking thefiber web which is held on the perforated patterning net while applying5 kcal/kg or more of heat to the fiber web in a heat application zonesimultaneously with or before or after the sucking of the fiber web; andthen drying the fiber web in a drying zone to obtain patterned bulkypaper.

The above objects are also accomplished by providing a process forproducing bulky paper comprising the steps of transferring a fiber webhaving a water content of 50 to 99% by weight to a patterning zone whichis provided before a drying zone and has a suction unit and a perforatedpatterning net revolving along the suction unit; patterning the fiberweb in conformity to the perforated patterning net by sucking the fiberweb which is held on the perforated patterning net; and then drying thefiber web in the drying zone to obtain patterned bulky paper,

the perforated patterning net comprising a reinforcing carrier belt anda perforated patterning structure which is disposed on the reinforcingcarrier belt and on which the fiber web is to be built up,

the reinforcing carrier belt having an individual opening area of 0.01to 10 mm², an open area ratio of 10 to 70%, and a tensile strength of 20kg/cm or more in the longitudinal direction thereof, and

the perforated patterning structure having an individual opening area of3 to 25 mm² and an open area ratio of 18 to 96%, a least width of 0.1 to5 mm in the pattern-forming constituent parts thereof in the planardirection, and a thickness of 0.3 to 1.5 mm.

The above objects are also accomplished by providing a process forproducing bulky paper comprising the steps of transferring a fiber webhaving a water content of 50 to 99% by weight to a patterning zone whichis provided before a drying zone and has a suction unit and a perforatedpatterning net revolving along the suction unit; patterning the fiberweb in conformity to the perforated patterning net by sucking the fiberweb which is held on the perforated patterning net; and then drying thefiber web in the drying zone to obtain patterned bulky paper,

the perforated patterning net having an individual opening area of 3 to8 mm², an open area ratio of 15 to 65%, a least width of 0.2 to 5 mm inthe pattern-forming constituent parts thereof in the planar direction, athickness of 0.5 to 3.0 mm, and a tensile strength of 20 kg/cm or morein the longitudinal direction thereof

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic illustration of the apparatus used in a firstembodiment of the bulky paper production process according to thepresent invention.

FIG. 2(a) is an enlarged partial plan view of a perforated patterningnet, and FIG. 2(b) is a cross sectional view taken along line I—I ofFIG. 2(a).

FIG. 3 is an enlarged partial view illustrating the state of a fiber webbeing sucked on a suction drum.

FIG. 4 is a schematic view showing the cross section of bulky paperobtained by the bulky paper production process according to the presentinvention.

FIG. 5(a) is an enlarged partial plan view of a perforated patterningnet used in a third embodiment, and FIG. 5(b) is a cross sectional viewtaken along line I—I of FIG. 5(a).

FIG. 6(a) is a plan view showing another example of a perforatedpatterning net used in the first embodiment (corresponding to FIG.2(a)), and FIG. 6(b) is a cross sectional view taken along line I—I ofFIG. 6(a) (corresponding to FIG. 2(b)).

THE BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the process for producing bulky paper accordingto the present invention will be described in detail with reference tothe drawings.

In FIG. 1 is shown an apparatus used in the first embodiment of thepresent invention. The apparatus (paper machine) 1 is an apparatus formanufacturing bulky paper having a patterning zone between a paper layerforming zone and a drying zone, the patterning zone having a suctiondrum 34, a steam spray nozzle N, and a perforated patterning net 31which revolves along a part of the peripheral surface of the suctiondrum 34. The apparatus 1 comprises a raw material feeding unit 10, apaper layer forming unit 20, a patterning unit 30, a drying unit 40, anda winding unit 50.

The raw material feeding unit 10 has a stock feed head 11. A fiberslurry having a prescribed concentration is fed from the stock feed head11 to the paper layer forming unit 20.

The paper layer forming unit 20 has a paper layer-forming belt 21 and asuction box 22 for dewatering which is provided in contact with thepaper layer forming-belt 21. The paper layer-forming belt 21 is a wiremesh belt used in general paper machines. The suction box 22 dewaters afiber web 2 formed on the paper layer-forming belt 21 to adjust thewater content of the fiber web 2 to be transferred to the downstreampatterning unit 30. A pickup carrier belt 23 runs over the zone from thepaper layer forming unit 20, through the patterning unit 30 to thedrying unit 40 to enable stable transfer of the fiber web 2. A suctionbox 24 serves to transfer the fiber web 2 from the paper layer-formingbelt 21 to the pickup carrier belt 23.

The patterning unit 30 has a suction drum 34, a steam spray nozzle N,and a perforated patterning net 31 which revolves along a part of theperipheral surface of the suction drum 34. As shown in FIGS. 2(a) and(b), the perforated patterning net 31 is composed of a reinforcingcarrier belt 33 made of a resin wire mesh and a perforated patterningstructure 32 which is superposed on the outer peripheral surface of thereinforcing carrier belt 33 and on which the fiber web 2 is held. Thesuction drum 34 contains inside a suction box 37. As shown in FIG. 1,the suction box 37 is placed inside the suction drum 34 at the positionwhere the perforated patterning net 31 runs in contact therewith so thatair may be sucked in through the perforated patterning net 31. The steamspray nozzle N is set outside the perforated patterning net 31 at theposition facing the suction box 37 so that steam may be sprayed over thewhole width of the fiber web 2. The patterning unit 30 has an air nozzle38 and a weak suction box 39 so that the fiber web 2 clinging to theperforated patterning net 31 can easily be transferred to the pickupcarrier belt 23.

In the patterning unit 30, the steam spray nozzle N is designed to spraysteam to the fiber web 2 at a prescribed temperature at a prescribedflow speed. Since the steam spray nozzle N faces the suction box 37 inthis embodiment as stated above, heat application by steam spraying ontothe fiber web 2 and suction of the fiber web 2 are carried outsimultaneously.

In order to impart a pattern to the wet fiber web 2 by suction, it isimportant to provide a patterning zone having the perforated patterningnet 31, the suction drum 34,, and the steam spray nozzle N. Thepatterning zone can be at any position between the paper layer formingzone and the drying zone of the apparatus 1.

The drying unit 40 has a drum-shaped through air drier (hereinafterreferred to as a drier) 41 which is designed to allow hot air to passtherethrough from the outside into the inside. A mesh net 42 is attachedto the peripheral surface of the drier 41. The net 42 has such a meshsize as causes no hindrance to the passage of hot air. A suction box 43is provided inside the drier 41 near the lower portion thereof therebyto facilitate transfer of the fiber web 2 coming from the patterningunit 30 to the net 42. The winding unit 50 has a winder 51 for taking upproduced bulky paper 3.

As described above, the perforated patterning net 31 is composed of theperforated patterning structure 32 and a reinforcing carrier belt 33.The perforated patterning structure 32 is a plastic net prepared by meltextrusion of a thermoplastic resin. It has a large number of circularopenings over the entire area thereof to form a mesh pattern. Theperforated patterning structure 32 and the reinforcing carrier belt 33are united into one body by sewing.

The openings 35 of the perforated patterning structure 32 shown in FIGS.2(a) and (b) each preferably have an area of 3 to 25 mm². With theindividual opening area being 3 mm² or wider, fibers are sufficientlyobliquely oriented into the openings 35 to form satisfactory low-densityprojections (corresponding to the regions with a low fiber density,hereinafter described) in bulky paper. With the opening area being 25mm² or smaller, the fibers are effectively prevented from falling off tomake holes, and formation of high-density regions (corresponding to theregions with a high fiber density, hereinafter described) in a meshpattern is secured sufficiently to efficiently provide bulky paper withsufficient strength. It is still preferred for each opening to have anarea of 4 to 10 mm², particularly 5 to 8 mm².

The area of the individual openings 35 is related to the open area ratioof the perforated patterning structure 32. It is preferred for theopenings 35 not only to have an individual area falling in theabove-described range but to have a total area in a ratio of from 18 to96%, particularly 40 to 87%, especially 50 to 75%, from the standpointof absorption capacity, texture, and strength of the bulky paper. Theterm “open area ratio” as used herein means the value measured as foronly the portion of the perforated patterning structure 32 where theopenings 35 are made. For example, both side portions of the perforatedpatterning structure 32 where the openings 35 are not formed areexcluded from the object of measurement.

The area of the individual openings 35 is also related to the width ofthe net-constituent parts 36 which form (surround) the individualopenings 35 (see FIGS. 2(a) and (b)). From the viewpoint of strength andtexture of the bulky paper, it is preferred not only that the openings35 have an individual area falling within the above-described range butthat the constituent parts 36 have a least width of 0.1 to 5 mm,particularly 0.2 to 2 mm, especially 0.3 to 1 mm, in the planardirection (i.e., in the plan view of the perforated patterning structure32). In cases where the constituent part has a varied width (e.g., wherethe perforated patterning structure 32 has a circular openings as shownin FIGS. 2(a) and (b)), the term “a least width” as used herein meansthe narrowest width in the plan view of that part. Where the constituentpart has a constant width in its plan view, that width is meant by thisterm.

It is also preferred for the perforated patterning structure 32 to havea thickness T (see FIG. 2(b)), namely the depth of the openings 35, of0.3 to 1.5 mm, particularly 0.4 to 1.0 mm, especially 0.5 to 0.8 mm.With the thickness being 0.3 mm or more, fibers are sufficientlydirected toward the openings 35, and low-density projections can beformed in the resulting bulky paper more easily. With the thicknessbeing 1.5 mm or smaller, the bulky paper is effectively prevented fromsuffering from holes.

It is preferred for the perforated patterning structure 32 to be waterrepellent for securing stability in papermaking (i.e., releasability ofthe fiber web 2 clinging to the perforated patterning net 31). It isstill preferred for the perforated patterning structure 32 to have suchwater repellency as makes a contact angle of 60° or more, particularly75° or more, with water. By using a perforated patterning net havingsuch a perforated patterning structure, the fiber web which once clingsto the perforated patterning net by suction patterning can be releasedmore easily from the perforated patterning net when transferred to theother carrier belt, which is more suitable to high-speed papermaking.Where the material of the perforated patterning structure 32 ishydrophilic, the above water repellency is preferably obtained bytreatment with a water-repellent coating. Specifically, the treatmentincludes a surface treatment with Teflon resins, urethane resins, etc.The releasability can also be improved by spraying on the perforatedpatterning structure a release agent such as polyolefin release agents,higher fatty acid release agents and mineral oil release agents. Thecontact angle as referred to above is determined by dropping 10 μl ofwater on a specimen (76 mm by 26 mm) of a perforated patterningstructure by means of a syringe and immediately thereafter measuring thecontact angle at 25° C. with Contact Anglemeter CA-D supplied by KyowaKaimen Kagaku.

The reinforcing carrier belt 33 which is used with the perforatedpatterning structure 32 in one body has a great number of openings 33′.It is used to enhance the strength of the perforated patterning net 31.For this purpose and for stable running of the perforated patterning neton the paper machine or the processing machine, the reinforcing carrierbelt 33 preferably has a tensile strength of 20 kg/cm or more,particularly 40 kg/cm or more, especially 60 kg/cm or more, in itslongitudinal direction (running direction). The tensile strength isobtained as a breaking strength in a tensile strength tester measuredunder conditions of 10 mm in width of a specimen, 100 mm in chuckdistance, and 60 mm/min in pulling speed. In order to secure asufficient air flow for imparting oblique orientation to fibers alongthe openings 35 of the perforated patterning structure 32 and asufficient strength as a carrier belt, the individual openings 33′preferably have an area of 0.01 to 1 mm². In order to effectivelyprevent the resulting bulky paper from suffering from holes in itslow-density projections, the opening area is still preferably 0.02 to 1mm², particularly preferably 0.03 to 0.3 mm². For obtaining a sufficientair flow for imparting oblique orientation to the fibers along theopenings 35 of the perforated patterning structure 32 and for obtainingsufficient strength as a carrier belt, the open area ratio of thereinforcing carrier belt 33 is preferably 10 to 70%, still preferably 15to 50%, particularly preferably 18 to 25%. The least width of theconstituent parts 33″ of the reinforcing carrier belt 33 in the planardirection is preferably 0.05 to 1 mm, still preferably 0.10 to 0.30 mm.The reinforcing carrier belt 33 can be of the same type as a mesh beltwoven of wires which is commonly used as a carrier belt for paper makingand processing.

The sewing for uniting the perforated patterning structure 32 and thereinforcing carrier belt 33 according to the present embodiment ispreferably carried out in such a manner as to leave no gap between thereinforcing carrier belt 33 and the perforated patterning structure 32.The method for uniting is not limited to sewing. For example, heatfusion can be used, or the perforated patterning structure 32 can beformed on the reinforcing carrier belt 33 by using a photosensitiveresin.

The bulky paper production process by the use of the apparatus 1 shownin FIG. 1 will be described further. A fiber suspension is fed from thestock feed head 11 onto the paper layer-forming belt 21 to build upfibers on the paper layer-forming belt 21 to form a wet fiber web (paperlayer) 2. The concentration of the fiber suspension is not limited andcan be selected appropriately from the range capable of stablyperforming the paper layer forming step.

The water content in the fiber web 2 is reduced by the suction boxes 22to adjust the water content of the fiber web 2 to be sent to thedownstream patterning zone to a prescribed level. The water content isadjusted to 50 to 85% by weight, preferably 65 to 75% by weight, basedon the weight of the fiber web 2 (i.e., the wet fiber web) to make itpossible to sufficiently pattern the fiber web 2 in the patterning step.With the water content falling within this range, oblique-orientedfibers are effectively obtained by suction, and the effect of heatapplication in raising the temperature of water is exerted sufficiently.

The fiber web 2 having its water content adjusted to a prescribed valueis separated from the paper layer-forming belt 21 and transferred to theperforated patterning structure 32 of the perforated patterning net 31.In the suction drum 34 which is inside the revolving perforatedpatterning net 31, air is drawn in by means of the suction box 37 fromthe outside into the inside through the perforated patterning net 31.Accordingly, the areas of the fiber web 2 that are positioned over theopenings 35 of the perforated patterning structure 32 (the areas willhereinafter be referred to as areas A) are sucked in the openings 35 bythe suction to form convexities with the thickness increasing toward theinside of the suction box 37 as shown in FIG. 3. The areas A becomeareas of low fiber density, where the constituent fibers are less densethan before the suction. Underneath the perforated patterning structure32 there is a reinforcing carrier belt 33 whose mesh is finer than thatof the perforated patterning structure 32. Therefore, an abrupt increasein thickness (i.e., an abrupt decrease in density) in the areas A isrestricted by the reinforcing carrier belt 33 so as not to make a bighole in the areas A or not to break the fiber web 2.

The areas of the fiber web 2 that are on the constituent parts 36 of theperforated patterning structure 32 and the vicinities of these areas(hereinafter these areas will be referred to as areas B) are pressedonto the constituent parts 36 and thus compressed by the suction and, asa result, get slightly thinner and denser than before suction. That is,the areas B become areas of higher fiber density relative to the areasA. These areas of high fiber density serve to suppress the tendency ofthe resulting bulky paper to show reduction in tensile strength due tothe areas of low fiber density. Since the perforated patterningstructure 32 has a continuous mesh pattern, the areas of high fiberdensity are also continuous, forming a mesh pattern, to further improvethe tensile strength of the resulting bulky paper.

Simultaneously with the suction, steam is sprayed from the steam spraynozzle N to supply the fiber web 2 with 5 kcal/kg or more of heatthereby to raise the temperature of water in the fiber web 2 and toshorten the drying time. As a result, the areas A and B have enhancedshape retention, and the spraying pressure of steam facilitatesformation of the areas A and B, thereby the fiber web 2 can be patternedmore clearly. If the quantity of heat applied to the fiber web 2 is lessthan 5 kcal/kg, the temperature rise of the water contained in the fiberweb 2 is insufficient, and the patterning of the fiber web 2 is notsufficient. A preferred range of the quantity of heat applied to thefiber web 2 is from 10 to 70 kcal/kg. In the present invention, the term“quantity of heat” is the quantity of heat applied per kilogram of thewet fiber web measured immediately before the heat application. Thequantity of heat is calculated from the temperature difference betweenthe fiber web 2 before and after passing through the heat applicationzone and the water content before passing through the heat applicationzone, defining the specific heat of the pulp and that of water as 0.4cal/g and 1.0 cal/g, respectively. That is, the water content of thefiber web 2 before passing through the heat application zone and thetemperature difference between before and after passing through the heatapplication zone being taken as x (wt %) and t (° C.), respectively, thequantity of heat Q (kcal/kg) applied to the fiber web 2 is representedby equation:

Q={0.4(1−x/100)+x/100}×t

The temperature and flow of the steam sprayed to the fiber web 2 are notparticularly limited as long as the heat quantity given to the fiber web2 is the above-specified value or higher. It is generally preferred thatthe steam immediately after being emitted from the nozzle has atemperature of 100° C. or higher and a flow rate of 2 m/sec or more,particularly 5 m/sec or more. While steam spray is used as a means forapplying heat to the fiber web 2 in this particularly embodiment, othermeans, such as a hot air blow may be used. In this case, it is preferredfor hot air to have a temperature of 50 to 300° C., particularly 100 to250° C., and a flow rate of 2 m/sec or more, particularly 5 m/sec ormore. The quantity of heat applied increases as the distance between thesteam nozzle or the hot air nozzle and the fiber web 2 decreases. Asuitable distance is 20 to 200 mm.

In this way, the fiber web 2 is given the pattern corresponding to themesh pattern of the perforated patterning structure 32 as the perforatedpatterning net 31 runs along part of the peripheral surface of thesuction drum 34.

The suction force of the suction box 37 in the patterning step, whiledependent on the basis weight, the water content, etc. of the fiber web2, preferably ranges, in general, from −10 to −100 kPa, particularly −25to −70 kPa.

The fiber web 2 given a prescribed pattern in the patterning step isthen introduced into a through air drier drum 41 of the drying zone,where it passes through hot air to dry. In this step, compressioncommonly carried out in ordinary papermaking process is not performed sothat the bulkiness of the bulky paper may not be impaired.

As the drier 41 makes approximately one revolution, the fiber web driesto give bulky paper 3 as a final product. The resulting bulky paper 3 iswound by means of the winder 51 of the winding unit 50.

As described above, according to the present embodiment the patterningzone having the suction unit, the heat application unit, and theperforated patterning net is provided before the drying zone, and heatis applied near the suction unit to improve pattern forming propertiesthereby to produce bulky paper excellent in bulkiness and absorbency.

The apparatus shown in FIG. 1 and the process of production using thesame present the following advantages (1) to (4).

(1) Since the perforated patterning net 31 revolves only about thesuction drum 34 with partial contact therewith, there is no need toprepare a net of very long size.

(2) The profile of the pattern to be imparted to the fiber web 2 can bechanged easily simply by exchanging the perforated patterning nets 31.

(3) Since the perforated patterning net 31 is not led into the dryingzone, it is hardly deteriorated even when used continuously for a longtime of period and therefore has a long lifetime.

(4) The apparatus can easily be switched to general papermaking toproduce plain paper by shifting the whole patterning unit 30 to removethe perforated patterning net 31 from the running line of the fiber web2.

A schematic cross section of the bulky paper thus produced is shown inFIG. 4. As shown in FIG. 4, the bulky paper 3 comprises areas A having alow fiber density and areas B having a high fiber density. The areas A,formed in conformity to the openings 35 of the perforated patterningstructure 32, have a relatively large thickness. On the other hand, theareas B, formed in conformity to the constituent parts 36 surroundingthe openings 35 of the perforated patterning structure 32, have arelatively small thickness. As a result, the bulky paper 3 is extremelybulky, having an uneven profile and a large thickness. Accordingly, itis highly absorbent and excellent in softness. The higher strength areasB making a continuous mesh pattern, the bulky paper 3 has moderatestrength.

The fiber which constitutes the bulky paper 3 is preferably short fibershaving a fiber length of 10 mm or less, particularly 0.5 to 5 mm. Suchshort fibers include wood pulp such as chemical pulp, semichemical pulp,mechanical pulp, etc. of softwood or hardwood; mercerized pulp orcrosslinked pulp prepared by chemically treating the wood pulp; non-woodfibers, such as flax and cotton; cellulose fibers such as regeneratedfibers, e.g., rayon fiber; and synthetic fibers, such as polyethylenefiber, polypropylene fiber, polyester fiber, and polyamide fiber. Ofthese fibers wood pulp, non-wood pulp, and cellulose fibers such asrayon fiber are preferred from the standpoint of product cost, strength,and suitability to papermaking. Wood pulp is still preferred from thestandpoint of product cost. These short fibers are preferably used in aproportion of 50 to 100% by weight, particularly 70 to 100% by weight,based on the total fiber constituting the bulky paper 3.

Where the bulky paper 3 is used as an absorbent base of cooking paper,paper towels, tissues, etc. or as a cleaning sheet to be impregnatedwith a detergent, etc., the bulky paper 3 preferably contains 50 to 100%by weight of the cellulose fiber based on the total fiber. It is alsopreferred for the bulky paper to additionally contain a wet strengthagent, such as polyamideamine epichlorohydrin resins, to exhibit wetstrength. Such a wet strength agent is, in general, preferably added inan amount of 0.2 to 2.0% by weight based on the total weight of thebulky paper. In order to obtain a higher wet strength, it is alsopreferred to use a mixed wet strength agent comprising theabove-mentioned polyamideamine epichlorohydrin resin mixed with ananionic polymer, such as carboxymethyl cellulose, or an ampholyticpolymer, such as ampholytic polyacrylamide.

A second and a third embodiments will then be described. The particularsof the second and the third embodiments that are the same as those ofthe above-described first embodiment are not explained here, and theexplanations given to the first embodiment apply thereto appropriately.The members of FIG. 5 that are the same as in FIGS. 1 to 4 are given thesame numerical references.

The difference of the second embodiment from the first one lies in thatthe heat application conducted on the fiber web 2 in the firstembodiment is not performed, that is, patterning of the fiber web 2 iseffected only by the perforated patterning net 31 composed of theabove-described reinforcing carrier belt 33 and the perforatedpatterning structure 32. In the second embodiment the water content ofthe fiber web to be forwarded to the patterning zone is adjusted to 50to 99% by weight, preferably 65 to 90% by weight, still preferably 70 to85% by weight. The reinforcing carrier belt has an individual openingarea of 0.01 to 1 mm , an open area ratio of 10 to 70%, and a tensilestrength of 20 kg/cm or more in its longitudinal direction. Theperforated patterning structure has an individual opening area of 3 to25 mm², an open area ratio of 18 to 96%, a least width of 0.1 to 5 mm inthe pattern-forming constituent parts thereof in the planar direction,and a thickness of 0.3 to 1.5 mm. While the combination of heatapplication and the perforated patterning net 31 secures sufficientpatterning of the fiber web 2 as mentioned above, it is still possibleto pattern the fiber web 2 with the perforated patterning net 31 aloneas will be apparent from Examples hereinafter given.

In the third embodiment, too, patterning is carried out with theperforated patterning net alone similarly to the second embodiment. Inthis embodiment, the fiber web before being transferred to thepatterning zone is adjusted to have a water content of 50 to 99% byweight, preferably 65 to 90% by weight, still preferably 70 to 85% byweight. The perforated patterning net used here has an individualopening area of 3 to 8 mm², an open area ratio of 15 to 65%, a leastwidth of 0.2 to 5 mm in the pattern-forming constituent parts thereof inthe planar direction, a thickness of 0.5 to 3.0 mm, and a tensilestrength of 20 kg/cm or more in the longitudinal direction thereof.

In more detail, the perforated patterning net 31 is a net woven ofresin-made wires (a plain weave net in the present embodiment) having agreat number of square openings 35 to form a mesh pattern over theentire area thereof as shown in FIGS. 5(a) and (b).

The openings 35 of the perforated patterning net 31 shown in FIGS. 5(a)and (b) each have an area of 3 to 8 mm², preferably 4 to 7 mm². If thearea is less than 3 mm², the fibers are not sufficiently obliquelyoriented along the openings 35, failing to form satisfactory low-densityprojections in the bulky paper. If the area exceeds 8 mm², the fibersmay fall off by suction, and it is likely that the resulting bulky paperhas holes. Further, the high-density areas formed in the bulky paper ina mesh pattern will have a reduced area, failing to provide bulky paperwith sufficient strength.

The open area ratio of the perforated patterning net 31 is 15 to 65%. Ifthe open area ratio is less than 15%, the total area of the areasforming the low-density projections will be reduced, failing to providebulky paper having a high absorption capacity and good texture. If theopen area ratio exceeds 65%, the total area of the high-density areaswill be reduced, failing to provide bulky paper with sufficientstrength. A preferred open area ratio is from 35 to 60%.

The least width, in the planar direction, of the net-forming constituentparts 36 of the perforated patterning net 31 is 0.2 to 5 mm. If theleast width is smaller than 0.2 mm, the high-density areas formed in theresulting bulky paper in a mesh pattern will be too narrow to providebulky paper with sufficient strength. If it exceeds 5 mm, thehigh-density areas formed in the resulting bulky paper in a mesh patternwill be too wide, only to provide paper with a hard texture. The leastwidth of the constituent parts 36 in the planar direction is preferably0.4 to 3 mm, still preferably 0.5 to 2.0 mm.

The perforated patterning net 31 has a thickness T (see FIG. 5(b)) of0.5 to 3.0 mm, preferably 0.7 to 2.5 mm, still preferably 1.0 to 2.0 mm.If the thickness T is smaller than 0.5 mm, the fibers are notsufficiently guided into the openings 35, failing to form satisfactorylow-density projections in the resulting bulky paper. If it exceeds 3.0mm, the fibers will not be obliquely oriented along the openings 35, andholes are liable to be formed in the bulky paper when a suction force isstrong.

Similarly to the first and second embodiments, it is preferred that theperforated patterning net 31 be water-repellent from the standpoint ofpapermaking stability. It is still preferred for the perforatedpatterning net 31 to have such water repellency as makes a contact angleof 60° or more, particularly 75° or more, with water.

Because the perforated patterning net 31 is made to revolve basicallyalone, it should have sufficient strength for withstanding therevolution. For this purpose, the perforated patterning net 31 isdesigned to have a tensile strength of 20 kg/cm or more, preferably 40kg/cm or more, still preferably 60 kg/cm or more, in the longitudinaldirection (i.e., in the running direction) thereof If the tensilestrength is less than 20 kg/cm, the perforated patterning net isincapable of running stably on the paper machine or the processingmachine.

The perforated patterning net 31 can be of the same type as a plasticnet woven of wires which is commonly used as a carrier belt for papermaking and processing as far as the above-mentioned conditions of areaof the individual openings, open area ratio, thickness and tensilestrength are fulfilled, and the least width of the constituent parts inthe planar direction ranges as defined above. Nets made of glass fiber,Kevlar fiber, metallic yarn, etc. are also employable.

The second and third embodiments offer the following advantage inaddition to the advantages (1) to (4) mentioned with reference to thefirst embodiments. Since patterning of the fiber web can be achievedwithout forwarding the perforated patterning net 31 to the drying zone,it is possible to use a perforated patterning net made of anon-heat-resistant material having a softening point of 250° C. orlower.

The present invention is not limited to the above-described embodiments.For example, the steam spray nozzle N used in the first embodiment maybe set in the upstream or downstream side of the suction box 37 in therunning direction of the fiber web 2 so that heat is applied to thefiber web 2 before or after the suction by the suction box 37.

The perforated patterning net integrally composed of the perforatedpatterning structure and the reinforcing carrier belt used in the firstembodiment may be replaced with a perforated patterning net consistingsolely of a single wire mesh belt as is used in the third embodiment.

The perforated patterning net used in the third embodiment includes notonly the one shown in FIGS. 5(a) and (b) that has square openings butalso one having rectangular or other shaped-openings or one having anarbitrary combination of these opening shapes. The perforated patterningnet may be used in combination with other mesh belts.

The apparatus used in each of the above-described embodiments can have aYankee drier between the drying unit 40 and the winding unit 50 and adoctor blade for craping at the outlet of the Yankee drier to furtherimprove the texture of the resulting bulky paper. In this case, it isdesirable to reduce the degree of drying the fiber web in the drier 41.

While the present invention has been described with reference to theembodiments in which the formed wet fiber web is patterned in the lineof a paper machine (in-line patterning), it is possible to adopt anembodiment in which papermaking is carried out in a usual manner, andthe paper obtained by general papermaking is re-wetted to make a fiberweb having the above-described water content, which is then patterned byuse of an apparatus having a perforated patterning net revolving along asuction part (off-line patterning).

Explanations relating to conventionally known papermaking techniquesappropriately apply to the particulars of the bulky paper productionprocess that have not been described in detail.

The present invention also provide the following embodiments.

An apparatus for producing bulky paper characterized by having apatterning zone which is provided before a drying zone and has a suctionunit, a heat application unit, and a perforated patterning net revolvingalong the suction unit.

A perforated patterning net having a large number of openings which isfor patterning a fiber web held thereon by suction, the fiber web havinga water content of 50 to 99% by weight, which is characterized in that:

the perforated patterning net is composed of a reinforcing carrier beltand a perforated patterning structure which is superposed on thereinforcing carrier belt and on which the fiber web is held,

the reinforcing carrier belt has an individual opening area of 0.01 to10 mm², an open area ratio of 10 to 70%, and a tensile strength of 20kg/cm or more in its longitudinal direction, and

the perforated patterning structure has an individual opening area of 3to 25 mm , an open area ratio of 18 to 96%, a least width of 0.1 to 5 mmin the pattern-forming constituent parts thereof in the planardirection, and a thickness of 0.3 to 1.5 mm.

An apparatus for producing bulky paper having a patterning zone which isprovided before a drying step and has a suction unit and a perforatedpatterning net revolving along the suction unit, which is characterizedin that:

the perforated patterning net is composed of a reinforcing carrier beltand a perforated patterning structure which is superposed on thereinforcing carrier belt and on which the fiber web is held,

the reinforcing carrier belt has an individual opening area of 0.01 to10 mm², an open area ratio of 10 to 70%, and a tensile strength of 20kg/cm or more in its longitudinal direction, and

the perforated patterning structure has an individual opening area of 3to 25 mm², an open area ratio of 18 to 96%, a least width of 0.1 to 5 mmin the pattern-forming constituent parts thereof in the planardirection, and a thickness of 0.3 to 1.5 mm.

A perforated patterning net having a large number of openings which isfor patterning a fiber web held thereon by suction, the fiber web havinga water content of 50 to 99% by weight, which is characterized in that:

the perforated patterning net has an individual opening area of 3 to 8mm², an open area ratio of 15 to 65%, a least width of 0.2 to 5 mm inthe pattern-forming constituent parts thereof in the planar direction, athickness of 0.5 to 3.0 mm, and a tensile strength of 20 kg/cm or morein its longitudinal direction.

An apparatus for producing bulky paper having a patterning zone which isprovided before a drying step and has a suction unit and a perforatedpatterning net revolving along the suction unit, which is characterizedin that:

the perforated patterning net has an individual opening area of 3 to 8mm², an open area ratio of 15 to 65%, a least width of 0.2 to 5 mm inthe pattern-forming constituent parts thereof in the planar direction, athickness of 0.5 to 3.0 mm, and a tensile strength of 20 kg/cm or morein its longitudinal direction.

EXAMPLES

The advantages of the present invention will be demonstrated by way ofExamples.

Examples 1

A mixed pulp raw material consisting of 60 wt % of softwood bleachedkraft pulp (NBKP; weight average fiber length: 2.35 mm) and 40 wt % ofhardwood bleached kraft pulp (LBKP; weight average fiber length: 0.74mm) was beaten by a refiner to a Canadian Standard Freeness (CSF) of 640ml. To a 2 wt % slurry of the pulp raw material were added 0.6 wt %(based on the weight of the pulp) of a polyamideamine epichlorohydrinresin WS-570 (produced by Nippon PMC) as a wet strength agent and 0.25wt % (based on the weight of the pulp) of carboxymethyl cellulose WS-A(produced by Dai-ichi Kogyo Seiyaku Co., Ltd.) as a dry strength agentand a yield improver for the polyamideamine epichlorohydrin resin toprepare a paper stock. Bulky paper was produced by using the preparedstock on the paper machine shown in FIG. 1. The paper layer-forming belt21 in FIG. 1 was a polyester belt of 1,4-satin weave (90 mesh/inch by 85mesh/inch).

The paper stock diluted to 0.1 wt % was fed from the stock feed head 11of the paper machine shown in FIG. 1 to the paper layer-forming belt 21and suction-dewatered by the suction box 22 to form a fiber web 2 havinga water content of 75 wt %. The fiber web 2 was forwarded to theperforated patterning net 31 revolving along part of the peripheralsurface of the suction drum 34 and sucked by the suction box 37 set inthe suction drum 34 under a force of −46.5 kPa. At the same time, steamwas sprayed onto the fiber web from the steam spray nozzle N which wasplaced on the periphery of the perforated patterning net 31 in theposition facing the suction box 37 thereby to impart a prescribedpattern to the fiber web. The quantity of heat applied to the fiber webwas 14.45 kcal/kg. The perforated patterning net 31 used here was madeby sewing together a resin net 32 having circular openings prepared bymelt extrusion of polypropylene and a reinforcing carrier belt 33(OS-80, produced by Nippon Filcon Co., Ltd.) as shown in FIGS. 2(a) and(b). The polypropylene net had a individual opening area of 7.1 mm², anopen area ratio of 65.3%, a width of 0.7 mm in the opening-formingconstituent parts thereof, and a thickness of 0.71 mm. The reinforcingcarrier belt had an individual opening area of 0.023 mm², an open arearatio of 18.8%, and a tensile strength of 67.7 kg/cm in its longitudinaldirection. The polypropylene resin had a contact angle with water of 92°so that the fiber web 2 might be easily released from the resin net 32.The papermaking speed in the bulky paper production was 150 m/min.

The patterned fiber web 2 was transferred to the pickup carrier belt 23by weak suction with the weak suction box 39 and sent into the drier 41,where the fiber web 2 was passed in hot air of 250° C. and dried toobtain bulky paper 3 having a basis weight of 22 g/m².

Example 2

Bulky paper having a basis weight of 22 g/m² was produced in the samemanner as in Example 1, except that the flow rate of steam wascontrolled to give 8.50 kcal/kg of heat to the fiber web.

Example 3

Bulky paper having a basis weight of 22 g/m² was produced in the samemanner as in Example 1, except for controlling the flow rate of steam togive 29.75 kcal/kg of heat to the fiber web and using, as the perforatedpatterning net 31, a net comprising a reinforcing carrier belt 33(OS-80, produced by Nippon Filcon Co., Ltd.) and a perforated patterningstructure 32 which is formed on the belt 33. The perforated patterningstructure 32 has square openings as shown in FIGS. 6(a) and (b),comprises a photosensitive resin (PVA and a tetrazonium salt) and iscoated with a urethane resin.

Example 4

Bulky paper having a basis weight of 22 g/m² was produced in the samemanner as in Example 1, except for controlling the flow rate of steam togive 32.30 kcav/kg of heat to the fiber web, using a single wire meshbelt as the perforated patterning net 31, and carrying out the suctionby the suction box 37 under a suction force of −33 kPa.

The wire mesh belt used was a net woven of resin-made wires (a plainweave net in this Example) to form a large number of square openings 35over the entire surface thereof in a mesh pattern. That is, this singlebelt performs the functions of the perforated patterning structure 32and the reinforcing carrier belt 33 used in Example 1.

Example 5

Bulky paper having a basis weight of 22 g/m² was produced in the samemanner as in Example 4, except that hot air of 200° C. was blown fromthe same nozzle N used for steam spraying onto the fiber web to apply11.05 kcal/kg of heat quantity.

The production conditions of the foregoing Examples are summarized inTable 1.In order to examine the thickness, strength and absorbingproperties of the bulky paper prepared in the foregoing Examples, theaverage dry thickness (under a load of 3 g/cm² or 23 g/cm²), the averagewet thickness (under a load of 3 g/cm² or 23 g/cm²), the dry tensilestrength (MD or CD), the wet tensile strength (MD or CD), and thesaturation water absorption per unit area were measured according to thefollowing methods. The results obtained are shown in Table 2.

Average Dry Thickness

An acrylic resin plate measuring 5 cm by 5 cm and weighing 75 g was puton a sheet of the bulky paper to give a load of 3 g/cm², and the averagedry thickness of the bulky paper under the load was measured with athickness meter (R5-C) supplied by Ozaki Seisakusyo. Further, an averagedry thickness of the bulky paper under a load of 23 g/cm² was measuredwith a 500 g weight put on the acrylic plate.

Average Wet Thickness

The bulky paper was cut to 7 cm by 7 cm. The cut piece was soaked in alarge amount of water for 5 seconds and then drained for 10 seconds. Theaverage wet thickness of the resulting wet piece was measured in thesame manner as in the measurement of the average dry thickness.

Dry Tensile Strength

The bulky paper was cut into a 25 mm wide and 100 mm long strip.Immediately thereafter, the strength at break was measured with auniversal compression tensile tester (RTM-25, manufactured by Orientec)at a pulling speed of 300 mm/min and a chuck distance of 50 mm. In Table2, MD indicates the strength in the running direction of the papermachine, and CD the strength in the crossing direction.

Wet Tensile Strength

The bulky paper was cut into a 25 mm wide and 100 mm long strip andsoaked in a large amount of water for 5 seconds and drained for 10seconds. The strength at break of the wet strip was measured in the samemanner as for the dry tensile strength.

Saturation Water Absorption

The bulky paper was cut into a 7 cm by 7 cm square and soaked in a largeamount of water for 20 seconds and drained for 30 seconds. The amount ofwater absorbed into the bulky paper (g/49 cm²) was measured with abalance.

TABLE 1 Example No. 1 2 3 4 5 Water Content (%) of Fiber Web Before 7575 75 75 75 Passing Through Suction Unit Temp. (° C.) of Fiber WebBefore 20 20 20 20 20 Passing Through Suction Unit Heat Source steamsteam steam steam hot air Temp. (° C.) of Fiber Web After 37 30 55 58 33Passing Through Suction Unit Heat Applied in Patterning (kcal/kg) 14.458.50 29.75 32.30 11.05 Suction Force in Patterning (kPa) −46.5 −46.5−46.5 −33 −33 Perforated Patterning Structure Shape of Openings circlecircle square square square Individ. Opening Area (mm²) 7.1 7.1 7.0 3.73.7 Open Area Ratio (%) 65.3 65.3 80.7 46.2 46.2 Least Width ofConstituent Parts (mm) 0.7 0.7 0.2 0.9 0.9 Thickness (mm) 0.71 0.71 0.551.8 1.8 Material polypropylene polypropylene PVA + polyester polyestertetrazonium salt Water Repellency Treatment — — urethane coating — —Contact Angle with Water (° C.) 92 92 83 77 77 Reinforcing Carrier BeltIndivid. Opening Area (mm²) 0.023 0.023 0.023 — — Open Area Ratio (%)18.8 18.8 18.8 — — Tensile Strength (kg/cm) 67.7 67.7 67.7 85 85 Methodof Uniting Perforated Patterning sewing sewing sewing — — Structure andReinforcing Carrier Belt

TABLE 2 Example No. 1 2 3 4 5 Average Dry Thickness (mm)  3 g/cm 0.750.71 0.70 0.77 0.72 23 g/cm 0.58 0.54 0.58 0.56 0.52 Average WetThickness (mm)  3 g/cm 0.60 0.58 0.59 0.58 0.55 23 g/cm 0.49 0.46 0.470.33 0.27 Dry Tensile Strength (g/25 mm) MD 1150 1150 1050 870 940 CD910 900 780 460 470 Wet Tensile Strength (g/25 mm) MD 350 350 350 260295 CD 210 220 210 185 190 Saturation Water Absorption 1.05 1.03 1.060.93 0.89 (g/49 cm²)

As is apparent from the results shown in Tables 1 and 2, the bulky paperobtained by sucking a fiber web while applying a specific amount of heat(Examples 1 to 5) has a large thickness, high absorption, and moderatestrength.

Example 6

Bulky paper having a basis weight of 22 g/m² was obtained in the samemanner as in Example 1, except that heat application by steam was notconducted.

Example 7

Bulky paper having a basis weight of 22 g/m² was produced in the samemanner as in Example6, except for using a perforated patterning net 31made by sewing together a resin net 32 having rectangular openings whichwas prepared by melt extrusion of polypropylene and a reinforcingcarrier belt 33 (OS-80, produced by Nippon Filcon Co., Ltd.).

Example 8

Bulky paper having a basis weight of 22 g/m² was produced in the samemanner as in Example 6, except for using, as the perforated patterningnet 31, a reinforcing carrier belt 33 (OS-80, produced by Nippon FilconCo., Ltd.) having formed thereon a perforated patterning structure 32having square openings comprising a photosensitive resin (PVA and atetrazonium salt) and coated with a urethane resin.

Example 9

Bulky paper having a basis weight of 22 g/m² was produced in the samemanner as in Example 6, except for using a perforated patterning net 31made by sewing together a perforated patterning structure 32 havingsquare openings which comprises a leno weave net of flat glass fiberscoated with a Teflon resin and a reinforcing carrier belt 33 (OP-18K,produced by Nippon Filcon Co., Ltd.).

Example 10

Bulky paper having a basis weight of 22 g/m² was produced in the samemanner as in Example 6, except for using a perforated patterning net 31made by sewing together the polypropylene resin net 32 used in Example 6and a reinforcing carrier belt 33 (OP-8, produced by Nippon Filcon Co.,Ltd.).

Comparative Example 1

Bulky paper having a basis weight of 22 g/m² was produced in the samemanner as in Example 6, except that the suction by the suction box 37was not carried out.

Comparative Example 2

Bulky paper having a basis weight of 22 g/m² was produced in the samemanner as in Example 6, except for using a perforated patterning net 31made by sewing together a polypropylene resin net 32 having squareopenings which was prepared by melt extrusion and a reinforcing carrierbelt 33 (OS-80, produced by Nippon Filcon Co., Ltd.).

The production conditions of the foregoing Examples and ComparativeExamples are summarized in Table 3. The average dry thickness (under aload of 3 g/cm² or 23 g/cm²), the average wet thickness (under a load of3 g/cm² or 23 g/cm²), the dry tensile strength (MD or CD), the wettensile strength (MD or CD), and the saturation water absorption perunit area of the bulky paper of the foregoing Examples and ComparativeExamples were measured. The results of the measurements are shown inTable 4.

TABLE 3 Example No. Compara. Example No. 6 7 8 9 10 1 2 Water Content(%) of Fiber 75 75 75 75 75 75 75 Web Before Suction Patterning SuctionForce in Patterning −46.5 −46.5 −46.5 −46.5 −46.5 0 −46.5 (kPa) (nosuction) Perforated Patterning Structure Shape of Openings circlerectangular square square circle circle square Individ. Opening Area(mm²) 7.1 4.5 7.0 20 7.1 7.1 1.6 Open Area Ratio (%) 65.3 47 80.7 66.865.3 65.3 68.4 Least Width of Constituent 0.7 1.0 0.2 1.0 0.7 0.7 0.25Parts (mm) Thickness (mm) 0.71 1.5 0.55 1.05 0.71 0.71 0.51 Materialpolypropylene polypropylene PVA + glass fiber polypropylenepolypropylene polypropylene tetrazonium salt Water Repellency Treatment— — urethane coating Teflon coating — — — Contact Angle with Water 92 9283 77 92 92 92 (° C.) Reinforcing Carrier Belt Individ. Opening Area(mm²) 0.023 0.023 0.023 0.74 3.74 0.023 0.023 Open Area Ratio (%) 18.818.8 18.8 36.8 46.2 18.8 18.8 Tensile Strength (kg/cm) 67.7 67.7 67.7130.0 85.0 67.7 67.7 Method of Uniting Perforated sewing sewing resinadhesion sewing sewing sewing sewing Patterning Structure andReinforcing Carrier Belt

TABLE 4 Compara. Example No. Example No. 6 7 8 9 10 1 2 Average DryThickness (mm)  3 g/cm 0.66 0.57 0.62 0.78 0.69 0.28 0.35 23 g/cm 0.510.45 0.49 0.58 0.52 0.16 0.27 Average Wet Thickness (mm)  3 g/cm 0.550.47 0.52 0.65 0.55 0.16 0.29 23 g/cm 0.44 0.40 0.41 0.51 0.44 0.14 0.20Dry Tensile Strength (g/25 mm) MD 1100 1250 1070 720 970 1950 1740 CD870 960 790 460 750 1300 1220 Wet Tensile Strength (g/25 mm) MD 340 360355 220 310 570 520 CD 210 230 220 155 190 390 360 Saturation WaterAbsorption 0.97 0.86 0.95 1.06 0.99 0.62 0.69 (g/49 cm²)

As is apparent from the results shown in Tables 3 and 4, the bulky paperobtained in a specific method by using a specific perforated patterningnet (Examples 6 to 10) has a large thickness, high absorption, andmoderate strength compared with the comparative paper.

Example 11

Bulky paper having a basis weight of 22 g/m² was obtained in the samemanner as in Example 1, except that the heat application with steam wasnot carried out and that the perforated patterning net 31 was a meshbelt woven of polyester resin wires in a plain weave which had squareopenings as shown in FIGS. 5(a) and (b), an individual opening area of3.7 mm², an open area ratio of 46.2%, a width of 0.9 mm in theopening-forming constituent parts thereof, a thickness of 1.8 mm, and atensile strength of 85 kg/cm in the longitudinal direction thereof Thecontact angle of the mesh belt with water was 77°.

Examples 12 and 13

Bulky paper having a basis weight of 22 g/m² was produced in the samemanner as in Examples 11, except for using the perforated patterning net31 shown in Table 5.

Comparative Example 3

Bulky paper having a basis weight of 22 g/m² was produced in the samemanner as in Example 11, except that the suction by the suction box 37was not conducted.

Comparative Example 4

Bulky paper having a basis weight of 22 g/m² was produced in the samemanner as in Example 11, except for using the perforated patterning net31 shown in Table 5.

The production conditions of the foregoing Examples and ComparativeExamples are summarized in Table 5. The average dry thickness (under aload of 3 g/cm² or 23 g/cm²), the average wet thickness (under a load of3 g/cm² or 23 g/cm²), the dry tensile strength (MD or CD), the wettensile strength (MD or CD), and the saturation water absorption perunit area of the bulky paper of the foregoing Examples and ComparativeExamples were measured. The results of the measurements are shown inTable 6.

TABLE 5 Compara. Example No. Example No. 11 12 13 3 4 Water Content (%)of Fiber 75 75 75 75 75 Web Before Suction Patterning Suction Force inPatterning (kPa) −33 −33 −33 0 −33 (no suction) Perforated PatterningStructure Shape of Openings square square square square square Individ.Opening Area (mm²) 3.7 5.5 7.9 3.7 2.3 Open Area Ratio (%) 46.2 56.053.8 46.2 39.4 Least Width of Constituent Parts (mm) 0.9 0.80 1.0 0.90.7 Thickness (mm) 1.8 1.5 2.3 1.8 1.8 Tensile Strength (kg/cm) 85 70 8285 110 Material polyester polyester polyester polyester polyesterContact Angle with Water (° C.) 77 77 77 77 77

TABLE 6 Compara. Example No. Example No. 11 12 13 3 4 Average DryThickness (mm)  3 g/cm 0.68 0.74 0.81 0.30 0.40 23 g/cm 0.48 0.52 0.580.16 0.27 Average Wet Thickness (mm)  3 g/cm 0.51 0.55 0.60 0.18 0.37 23g/cm 0.20 0.23 0.25 0.15 0.20 Dry Tensile Strength (g/25 mm) MD 960 890850 1870 1370 CD 470 450 430 1240 950 Wet Tensile Strength (g/25 mm) MD280 240 220 560 460 CD 190 170 160 370 320 Saturation Water Absorption0.84 0.90 0.95 0.64 0.72 (g/49 cm²)

As is apparent from the results shown in Tables 5 and 6, the bulky paperobtained in a specific method by using a specific perforated patterningnet (Examples 11 to 13) has a large thickness, high absorption,. andmoderate strength compared with the comparative paper.

Industrial Applicability

As described above in detail, according to the bulky paper productionprocess of the present invention, pattern forming properties areimproved by heat application near the suction unit to provide bulkypaper with excellent bulkiness and absorbency.

Bulky paper having a large thickness, high absorbency, excellentsoftness, and moderate strength can be obtained.

Since the perforated patterning net only revolves along the suctionunit, the net does not need to be so long.

According to the bulky paper production process of the presentinvention, the pattern profile can be changed easily simply byexchanging the perforated patterning nets.

Because the perforated patterning net 31 is not led into the dryingzone, it is hardly deteriorated even when used continuously for a longtime and therefore has a long lifetime. Further, this allows use ofnon-heat-resistant materials.

General papermaking can easily be carried out with the system simply byshifting the patterning unit out of the running line of the fiber web.That is, switching to general papermaking is easy.

What is claimed is:
 1. A process for producing paper in bulk comprising the steps of: forming a fiber web with a paper layer forming process; transferring said fiber web having a water content of 50 to 85% by weight to a patterning zone having a perforated patterning net revolving along a suction unit; patterning said fiber web in conformity with said perforated patterning net by a suction force to said fiber web from said suction unit, said fiber web being held on said perforated patterning net while applying 5 kcal/kg or more of heat to said fiber web in a heat application zone simultaneously with or before or after the application of said suction force to said fiber web; and drying said fiber web in a drying zone to obtain a patterned bulk paper, wherein a pickup carrier belt indirectly transfers said fiber web between said patterning and said drying steps, and said perforated patterning net is not led into the drying zone.
 2. A process for producing paper in bulk according to claim 1, wherein said fiber web is dried by passing said fiber web through uncompressed hot air.
 3. A process for producing paper in bulk according to claim 1, wherein said heat application zone includes steam spraying or hot air blowing sections.
 4. The process for producing paper in bulk according to claim 1, said perforated patterning net comprising a reinforcing carrier belt and a perforated patterning structure being disposed on said reinforcing carrier belt and on which said fiber web is to be built up, said reinforcing carrier belt having an individual opening area of 0.01 to 10 mm², an open area ratio of 10 to 70%, and a tensile strength of 20 kg/cm or more in the longitudinal direction thereof, and said perforated patterning structure having an individual opening area of 3 to 25 mm², an open area ratio of 18 to 96%, a width of at least 0.1 to 5 mm in the pattern-forming constituent parts thereof in the planar direction, and a thickness of 0.3 to 1.5 mm.
 5. The process for producing paper in bulk according to claim 4, wherein said perforated patterning structure has a water repellency as to form a contact angle of 60° or more with water.
 6. The process for producing paper in bulk according to claim 1, said perforated patterning net having an individual opening area of 3 to 8 mm², an open area ratio of 15 to 65%, a width of at least 0.2 to 5 mm in the pattern-forming constituent parts thereof in the planar direction, a thickness of 0.5 to 3.0 mm, and a tensile strength of 20 kg/cm or more in the longitudinal direction thereof.
 7. A process for producing bulky paper according to claim 6, wherein said perforated patterning net has a water repellency as to form a contact angle of 60° or more with water.
 8. The process for producing paper in bulk according to claim 1, wherein the application of heat to said fiber web is carried out simultaneously with the sucking of said fiber web, and the quantity of heat applied to said fiber web is from 5 to 70 kcal/kg. 